The nature of small RNA biology is not well understood, and there is a need to develop additional tools to interrogate the factors involved. This proposal describes our efforts to develop novel methods for accomplishing this need in dopamine receptor expressing neurons. Our strategy is to create lentiviral sensors that 'sense'the expression level of small RNAs. We are using this strategy to interrogate the predicted mRNA targets present within UTRs, and also to modulate the activity of microRNAs in the brain. We also describe how we will generate thousands of individual lentivirus sensors to cells, in the form of a mixed-pool library- a significant advancement for the dissection of noncoding RNA function in mammals. PUBLIC HEALTH RELEVANCE: Inside each of our cells, there is a dark matter lurking. It takes the form of small RNAs, which have the power to regulate almost every aspect of our lives. Inside our brains, these small RNAs- known as microRNAs- likely regulate processes that intersect with our behaviors, including impulsivity, risk taking, stress responsivity, and vulnerability to drug abuse and addiction. However, little is known about how this works, and what are the genes involved. This proposal describes our efforts to develop novel methods for interrogating the biology of small RNAs in the brain.